mysql服务器cpu爆满解决办法_sql语句

碰到一个mysql cpu爆满的问题，简单记录下

mysql服务器cpu爆满解决办法_慢查询_02

步骤：

1、通过show processlist找到耗时最长的

mysql> show processlist;+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+| Id | User | Host            | db   | Command | Time | State        | Info                                                                                                 |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
| 19 | root | localhost:60604 | big  | Query   | 1533 | Sending data | SELECT count(*) num,city FROM `ih_user_temp` where city in (select city from ih_user_temp where city || 25 | root | localhost       | NULL | Query   |    0 | NULL         | show processlist                                                                                     |
+----+------+-----------------+------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)


2、先杀掉该进程

mysql> kill 19;Query OK, 0 rows affected (0.01 sec)


3、通过慢查询日志找到具体的sql语句

开启慢查询：

[mysqld]
slow_query_log=1  #开启慢查询
long_query_time=5 #慢查询时间
log-slow-queries = /var/log/mysql/slowquery.log #需有写入权限


4、使用explain 优化sql语句，

引起cpu过高的sql一般集中在order by、group by、批量insert、嵌套子查询等sql语句中


5、调整my.cnf的query_cache_size和tmp_table_size的值